1. Field of the Invention
The present invention relates to an automatic telephone answering apparatus for automatically receiving an incoming call, sending an outgoing message and recording a message of a calling party.
2. Description of the Prior Art
Conventional automatic telephone answering apparatuses are classified into an apparatus of a type (to be referred to as a direct type hereinafter) which is directly connected to a telephone line and an apparatus of a type (to be referred to as an indirect type hereinafter) which is not directly connected to the telephone line. Indirect type automatic telephone answering apparatuses have been commercially available due to a relationship with a telephone system at the very beginning of development. For example, a typical indirect type automatic telephone answering apparatus was earlier developed by the same inventor and published as U.S. Pat. No. 3,376,390. In such direct and indirect type automatic telephone answering apparatus, upon reception of an incoming call, a pulse or leakage flux generated by calling signal shall be detected. The detection signal is amplified, and an amplified signal energizes a relay to make a loop circuit of a telephone line. Recent commercially available telephone sets have a construction to decrease a pulse or flux. For this reason, the sensitivity of an amplifier in a pulse or flux detection system must be increased. However, when the amplifier sensitivity is increased, a pulse or flux from a power source of an electrical device such as as a fluorescent lamp, a vacuum cleaner, or an electric shaver is picked up by the amplifier which is then erroneously operated. In addition, the amplifier is erroneously operated by a pulse from a power line thereof when the automatic telephone answering apparatus is reset to the standby mode, thereby repeating erroneous operations.
It is considerably difficult to establish correspondence between the pulse or leakage flux detecting systems used by each type of telephone set. For this reason, the ringing tone is often picked up and detected to start the automatic telephone answering apparatus. However, in the answering apparatus wherein the tone is detected, the detecting system is erroneously started by a tone similar to the ringing tone. Such a tone includes a high pitched voice, a vehicle siren tone, or other ringing tone from an adjacent telephone set, thus degrading reliability of the automatic telephone answering apparatus.